What is the greatest common factor of $40$ and $10$ ? Another way to say this is: $\operatorname{gcf}(40, 10) = {?}$
Solution: The greatest common factor is the largest number that is a factor of both $40$ and $10$ The factors of $40$ are $1$ $2$ $4$ $5$ $8$ $10$ $20$ , and $40$ The factors of $10$ are $1$ $2$ $5$ , and $10$ Thus, the greatest common factor of $40$ and $10$ is $10$. $\operatorname{gcf}(40, 10) = 10$